Abstract: A technology related to a binder that exhibits good ionic conductivity, binding properties, and discharge retention rate is provided. An aqueous polyurethane resin dispersion for binders that are used in lithium secondary batteries is an aqueous polyurethane resin dispersion including a polyurethane resin dispersed in water, the polyurethane resin being obtained by reacting a polyisocyanate compound (a), a compound (b) having two or more active hydrogen groups, a compound (c) having a hydrophilic group and one or more active hydrogen groups, and a chain extender (d) . The compound (b) contains a polyolefin (b1) having two or more active hydrogen groups and a polycarbonate (b2) having two or more active hydrogen groups and having 6 or less consecutive carbon atoms. A crosslink density per molecular weight of 1,000 of a resin solid component contained in the aqueous polyurethane resin dispersion is 0.02 mol/kg or more and 0.28 mol/kg or less.

Abstract: Provided is a technique with high strength, superior ionic conductivity, and superior electrical characteristics. A lithium ion secondary battery includes a positive electrode, a negative electrode, and a polymer electrolyte. The polymer electrolyte contains a lithium salt, an ionic liquid, and a polymer. The ionic liquid contains a bis(fluorosulfonyl)imide anion as an anion component. The content of the lithium salt is 2 mol/kg or more and 6 mol/kg or less based on the sum of the content of the ionic liquid and the content of the polymer. The content of the polymer is 25% by mass or more and 40% by mass or less based on the sum of the content of the ionic liquid and the content of the polymer.

Abstract: A technique that can improve ionic conductivity is provided. An electrolyte includes an inorganic composite particle that is a composite of an inorganic particle with a compound having a betaine structure and one or more functional groups selected from a (meth)acryloxy group, a Si(OR)3 group (R is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms), and an Al(OR)2 group (R is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms).